A. Field of the Invention
The invention relates to an improved process for the preparation of nitrohalobenzenes by the nitration of the corresponding halobenzene.
B. The Prior Art
It is well known to produce nitrohalobenzenes (such as nitrochlorobenzene) from halobenzenes (such as monochlorobenzene) by reacting a halobenzene with nitric acid and a second acid selected from the group consisting of sulfuric acid, phosphoric acid, sulfonic acid and mixtures of the above.
Typical of such processes is that described by U.S. Pat. No. 3,077,502, a commercial translation of which is a three-reactor conversion wherein sulfuric acid and nitric acid, as well as monochlorobenzene, is fed into the first reactor, with heat being removed and temperature maintained at about 45.degree. C. Residence time is about 45 minutes in the first reactor, and the conversion level based on nitric acid is 85-90%. The contents of the first reactor overflow into the second reactor wherein temperature is maintained at about 65.degree. C. Residence time in the second reactor is about 45 minures, and the conversion level is about 90-95%. The contents of the second reactor overflow into a third reactor where temperature is maintained at about 70.degree. C. Residence time is about 60 minutes and conversion based on nitric acid is close to about 99.5%.
Sulfuric acid, at a starting mole ratio to nitric acid of about 2/1, takes up the water generated during the course of the reaction, and its concentration drops from about 85% to about 73.5% at the end of the reaction. The spent acid is removed from the product stream in an oil-acid separator, and is pumped to an acid dehydrator. The dehydrated sulfuric acid at about 85% concentration is returned to the process.
Any method for increasing the efficiency of this production would be a significant advance in the art and is an object of this invention.